Centrifugal blower

ABSTRACT

A centrifugal multi-blade fan has multiple blades about a rotational shaft and draws in air along the rotational shaft and then blows the air approximately perpendicular to the rotational shaft to reduce wind noise. A scroll casing encloses the multi-blade fan and defines a scroll-shaped airflow passage for directing the air blown from the multi-blade fan. The scroll casing has an intake opening and an outlet opening at a scroll end, in a downstream scroll casing portion. The scroll casing expands such that a flow passage cross-sectional area on the airflow downstream side is larger than that on an airflow upstream side. A ratio of a blade length to a diameter of the multi-blade fan is greater than or equal to 0.12, and an outer scroll casing radius, relative to the rotational axis, increases as a logarithmic spiral, its expansion angle being from 3.3° to 4.8°.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No. 10/192,131 filed on Jul. 10, 2002. This application is based upon, claims the benefit of priority of, and incorporates by reference the contents of prior Japanese Patent Applications No. 2001-215649 filed Jul. 16, 2001, and No. 2001-322201 filed Oct. 19, 2001.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a centrifugal blower having a centrifugal multiblade fan (abbreviated as a centrifugal fan hereafter) applied to a vehicular air-conditioning apparatus.

2. Description of the Related Art

Generally, centrifugal fans use a centrifugal force to take in air in an axial direction, and to blow the air outward in a radial direction. The air blown out from the centrifugal fan has an airflow of an axial direction component directed from an intake side to a counter-intake side.

In the invention disclosed in Japanese Patent Laid-Open Publication No. Hei. 5-195995, an expanded part for expanding an airflow passage on the counter-intake side is formed in the airflow passage outside a centrifugal fan, and a side wall on a side of the centrifugal fan is tilted as a tilted surface in the expanded part (See FIGS. 20A and 20B). FIG. 20B is an enlargement of the area noted by the circular portion XXB of FIG. 20A. With this construction, the air blown out from the centrifugal fan flows smoothly along the tilted surface as shown as a solid line in FIG. 20B, and generation of airflow flowing toward the inlet opening along the inner wall surface on the outer peripheral side is restrained. As a result, interference (collision) of air directly flowing from the centrifugal fan toward the inner wall surface on the outer peripheral side of the scroll casing, air blown outward in the radial direction, and the air flowing toward the inlet opening along the inner wall surface on the outer periphery side is prevented from reducing wind noise.

The inventors produced and examined the blower described in the publication above, investigated the flow of the air in detail, and found the following points.

When the quantity of the airflow blown out from the centrifugal fan is relatively large, the air flows as described above (the solid line in FIG. 20B) and a stable swirling flow is generated. When the quantity of the airflow blown out from the centrifugal fan is relatively small, the quantity of the airflow is not enough for air which has collided with a wall surface 74 f to flow along a wall surface 74 g and a tilted surface 74 h. Therefore, the flow does not extend over the entire expanded part, and a stable swirling flow is not generated. As a result, the flow becomes unstable, the airflow tends to be disturbed, and wind noise becomes worse.

SUMMARY OF THE INVENTION

In view of the foregoing problems, an object of the present invention is to provide a centrifugal blower which can sufficiently reduce the wind noise even when the airflow quantity is small.

To attain the above object, a centrifugal blower according to a first aspect of the present invention comprises a centrifugal multiblade fan provided with multiple blades about a rotational shaft for taking in air in an axial direction of the rotational shaft and blowing the air outward in a radial direction with respect to the rotational shaft. A scroll casing is used for storing the centrifugal multiblade fan, the scroll casing constituting a scroll-shaped airflow passage for channeling the air blown out from the centrifugal multiblade fan, and having an intake opening on one end in the axial direction of the rotational shaft, and an outlet opening on an airflow downstream side of a scroll end.

The centrifugal blower is characterized in that expanded parts, expanded in a direction parallel with the rotational shaft, are provided in the airflow passage such that a flow passage cross-sectional area on the airflow downstream side is larger than that on the airflow upstream side. Additionally, a ratio of a blade length of the blades to a diameter of the centrifugal multiblade fan is 0.12 and over, an outer peripheral radius of the scroll casing extends as a logarithmic spiral, and its expansion angle n is from 3.3° to 4.8°.

With this construction, noise is sufficiently reduced even when the airflow quantity is small as shown in FIGS. 8 and 9 as described below.

A centrifugal blower according to a second aspect of the present invention comprises a centrifugal multiblade fan provided with multiple blades about a rotational shaft for taking in air along an axial direction of the rotational shaft, and blowing the air outward in a radial direction. Additional components include a scroll casing for storing the centrifugal multi-blade fan, the casing constituting a scroll-shaped airflow passage for the air blown out from the centrifugal multiblade fan. Also evident are an intake opening on one end in the axial direction of the rotational shaft, and an outlet opening on the airflow downstream side of the scroll end. This centrifugal blower is characterized in that expanded parts, expanded in a direction parallel with the rotational shaft, are provided in the airflow passage such that a flow passage cross-sectional area on the airflow downstream side is larger than that on the airflow upstream side, a ratio of a blade length of the blades to a diameter of the centrifugal multiblade fan is 0.12 or above, an outer peripheral radius of the scroll casing extends as a logarithmic spiral, and its expansion angle is from 3.5° to 4.5°.

With this construction, airflow noise is sufficiently reduced even when the airflow quantity is small as shown in FIGS. 8 and 9 described below.

A dimension of the winding-end portion in the direction parallel with the rotational shaft is 1.1 times to 2.3 times a dimension of a nose in the scroll casing in the direction parallel with the rotational shaft in a third aspect of the invention. With this constitution, noise is sufficiently reduced even when the airflow quantity is small as shown in FIGS. 8 and 10 described below.

The dimension of the winding-end portion in the direction parallel with the rotational shaft is from 1.3 times to 2.1 times of the dimension of a nose in the scroll casing in the direction parallel with the rotational shaft in a fourth aspect of the invention. With this constitution, noise is sufficiently reduced even when the airflow quantity is small as shown in FIGS. 8 and 10 described below.

The airflow passage may be constituted so as to have an approximately rectangular cross-section in a fifth aspect of the invention. The airflow passage is constituted so as to have an approximately rectangular cross-section whose corners are formed as an arc (rounded internal corners) in a sixth aspect of the invention. With this constitution, since an unstable swirling flow is prevented from being generated at the corners in the airflow passage, and simultaneously, a generated swirling flow is circulated smoothly, the swirling flow is stabilized, and the noise is reduced.

A protrusion protruding toward the centrifugal multiblade fan is provided on the inner wall on the outer periphery of the scroll casing, and has an approximately triangular shape protruding toward the centrifugal multi-blade fan as seen from a primary flow direction of the air flowing through the airflow passage in a seventh aspect of the invention.

When the protrusion is provided at a part with which air with the highest flow rate of the air blown out from the centrifugal multiblade fan collides, the air blown out from the centrifugal multiblade fan is easily split into the inlet opening side and the outlet opening side. As a result, generation of a swirling flow is promoted, and wind noise is reduced.

A centrifugal blower according to an eighth aspect of the present invention comprises a centrifugal multiblade fan provided with multiple blades about a rotational shaft for taking in air along an axial direction of the rotational shaft, and for blowing the air outward in a radial direction. The blower also exhibits a scroll casing for storing the centrifugal multi-blade fan, constituting a scroll-shaped airflow passage for channeling and directing the air blown away from the centrifugal multi-blade fan. The blower has an intake opening on one end in the axial direction of the rotational shaft, and an outlet opening on an airflow downstream side of a scroll end. The centrifugal blower is characterized in that a ratio of a blade length of the blades to a diameter of the centrifugal multi-blade fan is 0.12 and over, a fan inlet opening angle of the centrifugal multi-blade fan is from 55° to 85°, a fan outlet opening angle of the centrifugal multi-blade fan is from 15° to 45°, and a fan advancing angle, which is an angle between a line connecting an inlet-opening-side end of the blade with the rotational center of the multiblade fan, and a line connecting an outlet opening end of the blade with the rotational center of the multi-blade fan, ranges from 40 to 10°. With this construction, noise is sufficiently reduced even when the airflow quantity is small as shown in FIGS. 16 to 19 described below.

It is preferable that a curvature radius of the blade on the inlet opening side is equal to or less than a curvature radius of the blade on the outlet opening side in a ninth aspect of the invention.

It is preferable that the blades have a shape for smoothly connecting curved surfaces having two or more curvature radii with one another in a tenth aspect of the invention.

An outer peripheral side radius of the scroll casing extends as a logarithmic spiral, and its expansion angle n is from 3.3° to 4.8° in an eleventh aspect of the invention.

With this constitution, noise is sufficiently reduced even when the airflow quantity is small as shown in FIG. 8, FIG. 9, and FIGS. 16 to 19 described below.

The outer peripheral radius of the scroll casing extends as a logarithmic spiral, and its expansion angle n is from 3.5° to 4.5° in a twelfth aspect of the invention.

With this constitution, noise is sufficiently reduced even when the airflow quantity is small as shown in FIG. 8, FIG. 9, and FIGS. 16 to 19 described below.

It is preferable that expanded parts, expanded in a direction parallel with the rotational shaft, are provided in the airflow passage such that a flow passage cross-sectional area on the airflow downstream side is larger than that on the airflow upstream side in a thirteenth aspect of the invention.

Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of an air-conditioning apparatus according to embodiments of the present invention;

FIG. 2 is a sectional view of a blower according to a first embodiment of the present invention;

FIG. 3 is a descriptive drawing for an outlet-opening angle β2;

FIG. 4 is a view seen from a direction indicated by an arrow A in FIG. 2;

FIG. 5 is a view seen from a direction indicated by an arrow B in FIG. 2;

FIG. 6A is a descriptive drawing for describing an air flowing effect of the present invention;

FIG. 6B is a descriptive drawing for describing an air flowing effect of the present invention;

FIG. 7 is a schematic drawing showing airflow in an airflow passage of a scroll casing;

FIG. 8 is a graph showing a relationship between specific noise level and blade length divided by fan diameter (L/D);

FIG. 9 is a graph showing a relationship between the specific noise level and an expansion angle;

FIG. 10 is a graph showing a relationship between the specific noise level and an expansion ratio in an axial direction;

FIG. 11 is a schematic drawing showing a sectional shape of an airflow passage according to a second embodiment of the present invention;

FIG. 12 is a schematic drawing showing a sectional shape of an airflow passage according to a third embodiment of the present invention;

FIG. 13 is a descriptive drawing showing an inlet-opening angle β1, an outlet-opening angle β2, and an advancing angle γ;

FIG. 14A is a descriptive drawing showing a relationship between the inlet-opening angle β1, the outlet-opening angle β2, the advancing angle γ, and airflow;

FIG. 14B is a descriptive drawing showing a relationship between the inlet-opening angle β1, the outlet-opening angle β2, the advancing angle γ, and airflow;

FIG. 15A is a descriptive drawing showing a relationship between the inlet-opening angle β1, the outlet-opening angle β2, the advancing angle γ, and the airflow;

FIG. 15B is a descriptive drawing showing a relationship between a large blade length and airflow;

FIG. 16 is a chart showing a relationship between the minimum specific noise level, the ratio of blade length to fan diameter L/D, and the airflow rate;

FIG. 17 is a chart showing a relationship between the fan inlet-opening angle β1, the specific noise level, and the airflow rate;

FIG. 18 is a chart showing a relationship between the fan outlet-opening angle β2, and the specific noise level; and a relationship between the fan-outlet-opening angle β2 and the airflow quantity;

FIG. 19 is a chart showing a relationship between the advancing angle γ and the specific noise level; and a relationship between the advancing angle γ and the airflow quantity; and

FIG. 20A is a perspective view of a blower according to the prior art; and

FIG. 20B is an enlarged view of encircled area XXB in FIG. 20A according to the prior art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT First Embodiment

A centrifugal blower is applied to a blower in a vehicle air-conditioning apparatus according to a first embodiment of the present invention. FIG. 1 is a schematic drawing of a vehicle air-conditioning apparatus 1 for a vehicle equipped with a water-cooled engine, and the centrifugal blower (abbreviated as a blower hereafter) according to the present invention.

An internal air intake opening 3 for taking in cabin air, and an external air intake opening 4 for taking in outside air are formed on an airflow upstream side of an air conditioner casing 2 forming an airflow passage. An intake-opening switching door 5 is provided for selectively opening and closing the intake openings 3 and 4. Drive means such as a servomotor, or manual operation opens and closes the intake-opening switching door 5.

A filter (not shown) for removing dust in the air, and a blower 7 according to the present invention are provided on the airflow downstream side of the intake-opening switching door 5. The blower 7 blows air drawn from both of the intake openings 3 and 4 to the individual outlet openings 14, 15, and 17 which will be described later.

An evaporator 9 for cooling the air blown out into a cabin is provided on the airflow downstream side of the blower 7, and the entire volume of air blown by the blower 7 passes through the evaporator 9. A heater core 10 for heating the air blown out into the cabin is provided on the airflow downstream side of the evaporator 9, and this heater core 10 uses the coolant for the engine 11 as a heat source to heat the air. The blower shown in FIG. 1 is a schematic drawing, and its detail will be described later.

A bypass passage 12 for bypassing the heater core 10 is formed in the air conditioner casing 2. An air mix door 13 for adjusting an airflow quantity ratio between an airflow quantity passing through the heater core 10, and an airflow quantity passing through the bypass passage 12 to adjust the temperature of the air blown into the cabin, is provided on the airflow upstream side of the heater core 10.

A face aperture 14 for blowing out the air-conditioned air to the upper body of passengers in the cabin, a foot aperture 15 for blowing out the air to the feet of the passengers in the cabin, and a defroster aperture 17 for blowing out the air on the inner surface of a windshield 16 are formed on an extreme airflow downstream side of the air conditioner casing 2.

Blow mode switching doors 18, 19, and 20 are provided on the airflow upstream side of the individual apertures 14, 15, and 17, respectively. Drive means such as a servomotor, or a manual operation opens and closes these blow mode switching doors 18, 19, and 20.

Generally, since a large airflow is required in a face mode where the air is blown out from the face aperture 14 for the vehicle air-conditioning apparatus, a draft resistance (a pressure loss) for the face mode is smaller than that for the other blow modes (a foot mode for blowing out the air from the foot aperture 15, and a defroster mode for blowing out the air from the defroster aperture 17).

The blower 7 is a centrifugal blower which draws in air parallel to the direction of a rotational shaft and blows it away from the shaft in a radial direction (perpendicular to the rotational shaft). A centrifugal multi-blade fan 72 (abbreviated as a fan hereafter) is made of resin (polypropylene in the present embodiment) or other plastic or metal, and has a large number of blades 71 about a rotational shaft. A boss 71 a is present for holding the multiple blades 71.

In the present embodiment, the fan 72 is a radial fan where a fan outlet opening angle (β2) of the blade 71 is more than 60°, and less than 120°, and the specification of the fan 72 is set such that the ratio of the blade length L of the blade 71 (see FIG. 3) to the diameter D of the fan 72 (see FIG. 2) (L/D) is 0.12 and higher (L/D=0.14 in the present embodiment).

The fan outlet opening angle β2 is an angle between the tangent line of the blade 71 and the tangent line of an outside edge of the fan 72, and is measured on a forward side of the rotational direction of the fan 72 as shown in FIG. 3. The blade length L of the blade 71 is a difference between the outside radius and the inside radius of the fan 72.

An electric motor 73 is driven to rotate the fan 72 in FIG. 2. A scroll casing 74 (abbreviated as a casing hereafter) stores the fan 72, and constitutes an airflow passage 74 a for circulating the air blown out from the fan 72.

As shown in FIGS. 4 and 5, the casing 74 is made of resin (polypropylene in the the airflow which changes direction from the inlet opening 75 toward the outside in the radial direction (perpendicular to the shaft), and is formed on an end of the blades 71 on the side of the inlet opening 75. An opposing bent wall 78 is formed on the casing 74 near the bellmouth 76, opposite to the shroud 77 with a predetermined gap 77 a, and smoothly bends from the bellmouth 76 toward the outside in the radial direction along the shape of the shroud 77.

In the airflow passage 74 a of the casing 74, the inner radius of the outer periphery r1 increases as a logarithmic spiral such that the flow passage cross-sectional area in the airflow downstream side (the side of the outlet opening 74) is larger than that in the airflow upstream side (the side of the nose 74 c in the casing 74). Simultaneously, expanded parts 74 d and 74 e expanded in the direction parallel with the rotational shaft are provided to gradually increase the flow passage cross-sectional area as shown in FIG. 2.

A dimension H1 of the winding-end portion parallel with the rotational shaft is from 1.3 times to 2.1 times, or from 1.1 times to 2.3 times (1.5 times in the present embodiment) a dimension H0 of the nose 74 c (at scroll angle θ=0) parallel with the rotational shaft. An expanded dimension Hup on the side of the inlet opening 75 is less than 0.4 times an expanded dimension HLR on the opposite side of the inlet opening 75 (0<Hup/HLR<0.4) in the expanded parts 74 d and 74 e.

The expanded dimension Hup on the side of the inlet opening 75 is a dimension from the inner wall on the side of the inlet opening 75 to an inner wall of an upper side expanded part in the casing 74 measured parallel with the rotational shaft as shown in FIG. 2. The upper side expanded part is a part of the casing 74 on the scroll end side shifted by the outer diameter dimension D of the fan 72 from a part corresponding to the rotational center (the rotation shaft) of the fan 72 toward the outlet opening 74 b as shown in FIG. 4.

The expanded dimension HLR on the opposite side of the inlet opening 75 is a dimension from the inner wall on the opposite side of the inlet opening 75 to an inner wall of a lower (far) side expanded part in the casing 74 measured parallel to (along) the rotational shaft. The lower side expanded part is a part of the casing 74 on the scroll end side shifted by the outer diameter dimension D of the fan 72 from the part corresponding to the rotation center (the rotation shaft) of the fan 72 to the outlet opening 74 b.

The expanded part 74 d out of the expanded parts 74 d and 74 e of the present embodiment expands the flow passage cross-sectional area on the side of the inlet opening 75, and is formed proximate the scroll end toward the outlet opening 74 b of the casing 74. The expanded part 74 e out of the expanded parts 74 d and 74 e expands the flow passage cross-sectional area on the opposite side of the inlet opening 75, and is formed from a range of a part up to about 60° from a neighborhood of the nose 74 c in the rotational direction of the fan 72 toward the outlet opening 74 b of the casing 74.

The following section describes characteristics (actions and effects) of the present embodiment. As described above in the summary of the invention, when the quantity of the airflow blown out from the fan 72 is relatively small, the quantity of the airflow is not enough for air which has collided with a wall surface 74 f to flow along a wall surface 74 g, and the tilted surface 74 h. Particularly, the flow does not move across or over the entire expanded part 74 e, and a stable swirling flow is not generated.

The air taken into the fan 72 flows into gaps between blades 71 from a direction tilted with respect to the height direction (the direction parallel with the rotational shaft) of the blades 71, and is blown out from the fan 72 as shown in FIGS. 6A and 6B.

Since the blade 71 does not add momentum to the airflow parallel to the rotational shaft between the blades 71, the air between the blades 71 has a constant velocity component in the rotational shaft direction. When the blade length L of the blade 71 increases (L1>L2), because a time required for air flowing out from the gap between the blades 71 after flowing thereinto increases, a travel distance of the air between the blades 71 in the rotational shaft direction increases (h1>h0).

When it is assumed that the airflow quantity blown out from the fan 72 is constant regardless of the blade length L, the flow rate of the air blown out from the fan 72 increases as the blade length L of the blade 71 increases. Thus, increasing the blade length L prevents a decrease of the flow rate of the air blown out from the fan 72 when the blown air quantity is small. As a result, the flow extends over the expanded part 74 e, a stable swirling flow is generated, and wind noise is reduced.

Since the airflow passage 74 a curves in a scroll shape, when the air flows along the airflow passage 74 a, a secondary flow (a swirling flow) is generated as shown in FIG. 7. Since the swirling flow of the air blown out from the fan 72 matches this secondary flow (the swirling flow), the swirling flow is more stably generated, and wind noise is reduced.

When the inventors measured the specific noise level using the ratio of the blade length L of the blade 71 to the diameter D of the fan 72 (L/D), the expansion angle n of the scroll and the expanding ratio in the axial direction (winding end portion with respect to the dimension H0 parallel to the rotational axis and nose portion 74 c within casing 74, and the dimension H1 (ratio H1/H0) which is parallel to the rotational axis) as parameters, the results as shown in FIG. 8 and FIG. 9 have been obtained.

FIG. 8 and FIG. 9 respectively show results when the cross-sectional area of the scroll air passage with respect to the winding direction angle θ are set as equal, but the expansion angle n and the expanding ratio in the axial direction are varied. Therefore, when the expansion angle n is large and the expansion ratio in the axial direction is 1.0, the cross-sectional shape of the air passage 74 a becomes oblong in the horizontal direction (perpendicular to the rotational shaft). To the contrary, when the expansion angle n is small, the expansion ratio in the axial direction becomes larger and the cross-sectional shape of the air passage 74 a becomes oblong in the vertical direction (parallel to the rotational shaft).

As clearly shown by the test results, when L/D is set to 0.12 and over, the expansion angle n is set to 3.3° and over and 4.8° and below, so the wind noise can be reduced.

As in the first embodiment, when the expansion angle n=4° and the expansion ratio in the axial direction is 1.5, the ratio of cross-section of air passage 74 a in length and breadth becomes approximately 2:1, which is a favorable shape in terms of a pair of swirling movement of the air flow situated above and below each other. Therefore, the airflow becomes stable and the wind noise can be greatly reduced.

On the other hand, when the expansion angle n is larger (n)>4.8°), the distance from the fan 72 to the wall surface 74 g (the outer peripheral side inner wall of the casing 74) becomes larger. Therefore, when the airflow amount is small, as in the foot mode, the momentum of air blown out from the fan 72 becomes small when it collides with the wall surface 74 g. As a result, swirling airflow is hardly generated. Also, when the expansion angle n is larger, the momentum of air blown out from the fan 72 becomes larger and swirling airflow is generated by making the blade length longer. However, since the cross-sectional shape of the air passage becomes oblong in the horizontal direction, there is not enough space for swirling movement. As a result, airflow becomes unstable and the noise cannot be reduced so much.

To the contrary, when the expansion angle n is smaller (n>3.3°), the cross-sectional shape of the airflow passage 74 a becomes oblong in the vertical direction. Therefore, when the airflow amount is small, as in the foot mode, the airflow does not reach the wall surface 74 g and stable swirling airflow is not generated. Also, even though the expansion angle n is small, the air reaches the wall surface 74 g by lengthening the blade length. However, the swirling airflow becomes oblong in the vertical direction and the airflow becomes unstable.

FIG. 10 shows a test result with a ratio of the dimension H1 to the dimension H0 (H1/H0) as a parameter, where H1 is the dimension of the winding-end portion parallel with the rotational shaft, and H0 is the dimension of the nose 74 c parallel with the rotational shaft in the casing 74. As the test results clearly show, when H1/H0 is 1.3 to 2.1, the specific noise level can be reduced. Here, FIG. 10 shows the test result when L/D=0.14 and the expansion angle n=4.0°.

The definition of the specific noise level follows JIS B 0132, and the test method is based on JIS B 8340.

In the present embodiment, L/D is set to 0.12 and over, the expansion angle n is set to from 3.5° to 4.5°, and H1/H0 is set from 1.3 to 2.1. However, the present embodiment is not limited to these conditions. It is only necessary to set L/D to 0.12 and over and to set the expansion angle n from 3.5° to 4.5°, or to set L/D to 0.12 and over, and to set H1/H0 from 1.3 to 2.1.

Second Embodiment

The cross-section of the flow passage 74 a can be set as an approximately rectangular shape whose corners are arcs in a second embodiment as shown in FIG. 11. With this structure, since an unstable swirling flow is prevented from being generated at the corners of the airflow passage 74 a, and simultaneously, a generated swirling flow is smoothly circulated, the swirling flow is stabilized, and wind noise is reduced. It is preferable that the curvature radius of the arcs is properly set according to the radius of the swirling flow generated in the airflow passage 74 a.

Third Embodiment

FIG. 12 shows a third embodiment of the present invention. A protrusion 74 j protruding toward the fan 72 is formed along almost the entire airflow passage 74 a on the inner wall of the outer peripheral portion of the casing 74, and the cross-section of the protrusion 74 j is approximately triangular (wedge-shaped) and protrudes toward the fan 72 when the protrusion 74 j is seen from a primary flow direction of the air flowing through the airflow passage 74 a.

With this structure, since the protrusion 74 j is provided at a part with which air with the highest flow rate of the air blown out from the fan 72 collides, the air blown out from the fan 72 is easily divided into the side of the inlet opening 75 and the opposite side. This promotes the generation of swirling flow to reduce wind noise generation.

Fourth Embodiment

In the present embodiment, the blade length L is extended to shift the air blown out from the fan 72 toward the opposite side of the inlet opening 75 for increasing the flow rate. Also, the air blown out from the fan 72 collides with the wall surface 74 f to generate a stable swirling flow as described above. In a fourth embodiment, L/D is set to 0.12 and over, a fan inlet opening angle β1 is set from 55° to 85°, a fan outlet opening angle β2 is set from 15° to 45°, and a fan advancing angle γ is set to 4° to 10°. With these settings, the air is prevented from separating from the blades 71 and from between the blades 71. Also, air counter-flow is prevented from forming between the blades 71 at the outlet opening side of the fan, and wind noise is reduced.

With reference to FIG. 13, the fan inlet opening angle β1 is an angle between the tangent line of the blade 71 and the tangent line of an inside edge of the fan 72, and is measured on the forward-facing side of the blade in the rotational direction of the fan 72 as shown in FIG. 13. The fan advancing angle γ is an angle between a line L1 connecting an end of the blade 71 closest to an inlet opening side with the rotational center of the fan 72 and a line L2 connecting an end of the blade 71 near an outlet opening side with the rotation center of the fan 72. That is, line L1 is drawn from the rotational center of the fan 72 tangent to a first end of the blade 71 that is closest to the rotational center. This first point of tangency is on the front side of the blade that leads during the rotation of the blade 71. The line L2 is drawn from the rotational center of the fan 72 tangent to a second end of the blade 71 farthest from the rotational center. This second point of tangency is on the front side of the blade 71 that leads during the rotation of the blade 71.

The following section describes characteristics (actions and effects) of the present embodiment.

FIG. 14A shows a state of the air flowing between the blades 71 when the fan inlet opening angle β1 is large (about 90°). When the fan inlet opening angle β1 is larger than an angle at which the air flows into the fan 72 (theoretical flow-in angle is about 30°), the air between the blades 71 is separated from the blade 71 on the forward side in the rotational direction. Thus, a flow rate distribution on the fan outlet opening side becomes uneven, and noise tends to be generated.

FIG. 14B shows a state of the air flowing between the blades 71 when the fan inlet opening angle β1 is set to the theoretical flow-in angle. In this state, though, the separation of the air from the blade 71 on the forward side in the rotation direction is prevented on the inlet opening side. However, when the fan advancing angle γ is small, the air separated from the blade 71 on the forward side in the rotation direction is blown out without being attached to the blade 71 again on the outlet opening side. As a result, a counter-flow is generated on the forward side in the rotation direction, and new noise may be generated.

In the present embodiment, L/D, the fan inlet opening angle β1, the fan outlet opening angle β2, and the fan advancing angle γ are set to proper values, and the separation on the inlet opening side is restrained, and simultaneously, the air separated from the blade 71 on the forward side in the rotational direction is attached again as shown in FIGS. 15A and 15B. As a result, the airflow between the blades 71 is optimized, a stable swirling flow is generated, and noise is reduced.

FIG. 16 represents a test result showing a relationship between L/D and the minimum specific noise level, and a relationship between L/D and the airflow rate. FIG. 17 represents a test result showing a relationship between the fan inlet opening angle β1 and the specific noise level, and a relationship between the fan inlet opening angle β1 and the airflow rate. FIG. 18 represents a test result showing a relationship between the fan outlet opening angle β2 and the specific noise level, and a relationship between the fan outlet opening angle β2 and the airflow rate. FIG. 19 represents a test result showing a relationship between the advancing angle γ and the specific noise level, and a relationship between the advancing angle γ and the airflow rate. The test conditions and the definitions of the technical terms are the same as those in the embodiments described above.

As these test results clearly show, L/D should be set to 0.12 and over (0.15 in the present embodiment), the fan inlet opening angle β1 should be set to from 55° to 85° (65° in the present embodiment), the fan-outlet-opening angle β2 should be set from 15° to 45° (35° in the present embodiment), and the fan advancing angle γ should be set from 4° to 10° (7° in the present embodiment).

In the present embodiment, the curvature radius r1 on the inlet opening side of the blade 71 is equal to or less than the curvature radius r2 on the outlet opening side of the blade 71, and curved surfaces having more than two curvature radii r1 and r2 are smoothly connected to form the blade 71 such that the fan inlet opening angle β1, the fan outlet opening angle β2, and the fan advancing angle γ satisfy the advantageous conditions described above. However, the present embodiment is not limited to this construction, and the curvature radius may increase gradually from the inlet opening side to the outlet opening side, or may be constant as long as the conditions above are satisfied.

The present embodiment may be combined with the embodiments described above. As shown in FIGS. 8 and 9, and FIGS. 16 to 19, L/D is set to 0.12 and over, the fan inlet opening angle β1 is set from 55° to 85°, the fan outlet opening angle β2 is set from 15° to 45°, the fan advancing angle γ is set from 4° to 10°, and the expansion angle n is set from 3.3° to 4.8°. Alternatively, L/D is set to 0.12 and over, the fan inlet opening angle β1 is set from 55° to 85°, the fan outlet opening angle β2 is set from 15° to 45°, the fan advancing angle γ is set from 4° to 10°, and the expansion angle n is set from 3.5° to 4.5°.

The present embodiment may be applied to a casing not including the expanded parts 74 d and 74 e (the dimension of the airflow passage 74 a parallel with the rotational shaft is constant).

Other Embodiments

While the tilted surface 74 h is provided in the expanded part 74 e in the first embodiment, the present invention is not limited to this construction, and the airflow passage may have other shapes such as a simple rectangle, a circle, and an ellipse. 

1. A centrifugal blower comprising: a centrifugal multi-blade fan having multiple blades about a rotational shaft, wherein said centrifugal fan takes in air along an axial direction of said rotational shaft and blows said air outward in a radial direction with respect to said rotational shaft; and a scroll casing for storing said centrifugal multi-blade fan, said scroll casing defining a scroll-shaped airflow passage for directing said air blown out from said centrifugal multi-blade fan, said scroll casing having an intake opening at a first end of said rotational shaft and an outlet opening at a scroll end at an airflow downstream portion; wherein a first expanded part and a second expanded part are expanded in a direction parallel with said rotational shaft and are provided in said airflow passage such that a flow passage cross-sectional area on the airflow downstream side is larger than that on an airflow upstream side; a ratio of a blade length of said blades to a diameter of the centrifugal multi-blade fan is equal to or over 0.12; an outer peripheral radius of said scroll casing expands as a logarithmic spiral, and its expansion angle is from 3.3° to 4.8°; a dimension of said winding-end portion in a direction parallel with said rotational shaft is from 1.1 times to 2.3 times a dimension of a nose in said scroll casing in a direction parallel with said rotational shaft.
 2. The centrifugal blower according to claim 1, wherein a dimension of said winding-end portion in a direction parallel with said rotational shaft is from 1.3 times to 2.1 times of a dimension of a nose in said scroll casing in a direction parallel with said rotational shaft.
 3. A centrifugal blower comprising: a centrifugal multi-blade fan provided with multiple blades about a rotational shaft for drawing in air along said rotational shaft and blowing said air outward in a radial direction, perpendicular to said rotational shaft; and a scroll casing for storing said centrifugal multi-blade fan, said scroll casing defining a scroll-shaped airflow passage for directing said air blown out from said centrifugal multi-blade fan, and said scroll casing defines an intake opening on a first end in the axial direction of said rotational shaft, and an outlet opening at an airflow downstream side of a scroll end; wherein a plurality of expanded parts extending in a direction parallel to said rotational shaft are provided in said airflow passage such that a flow passage cross-sectional area on the airflow downstream side is larger than that on an airflow upstream side; a ratio of a blade length (L) of said blades to a diameter of the centrifugal multi-blade fan is equal to or over 0.12; an outer peripheral radius of said scroll casing extends as a logarithmic spiral, wherein its expansion angle is from 3.5° to 4.5°; and a dimension of said winding-end portion in a direction parallel with said rotational shaft is from 1.1 times to 2.3 times a dimension of a nose in said scroll casing in a direction parallel with said rotational shaft.
 4. The centrifugal blower according to claim 3, wherein a dimension of said winding-end portion in a direction parallel with said rotational shaft is from 1.3 times to 2.1 times of a dimension of a nose in said scroll casing in a direction parallel with said rotational shaft.
 5. A centrifugal blower comprising: a centrifugal multi-blade fan having multiple blades about a rotational shaft, wherein said centrifugal fan takes in air along an axial direction of said rotational shaft and blows said air outward in a radial direction with respect to said rotational shaft; and a scroll casing for storing said centrifugal multi-blade fan, said scroll casing defining a scroll-shaped airflow passage for directing said air blown out from said centrifugal multi-blade fan, said scroll casing having an intake opening at a first end of said rotational shaft and an outlet opening at a scroll end at an airflow downstream portion; wherein a first expanded part and a second expanded part are expanded in a direction parallel with said rotational shaft and are provided in said airflow passage such that a flow passage cross-sectional area on the airflow downstream side is larger than that on an airflow upstream side; a ratio of a blade length of said blades to a diameter of the centrifugal multi-blade fan is equal to or over 0.12; an outer peripheral radius of said scroll casing expands as a logarithmic spiral, and its expansion angle is from 3.3° to 4.8°; said airflow passage has an approximately rectangular cross-section with rounded interior passage corners.
 6. A centrifugal blower comprising: a centrifugal multi-blade fan having multiple blades about a rotational shaft, wherein said centrifugal fan takes in air along an axial direction of said rotational shaft and blows said air outward in a radial direction with respect to said rotational shaft; and a scroll casing for storing said centrifugal multi-blade fan, said scroll casing defining a scroll-shaped airflow passage for directing said air blown out from said centrifugal multi-blade fan, said scroll casing having an intake opening at a first end of said rotational shaft and an outlet opening at a scroll end at an airflow downstream portion; wherein a first expanded part and a second expanded part are expanded in a direction parallel with said rotational shaft and are provided in said airflow passage such that a flow passage cross-sectional area on the airflow downstream side is larger than that on an airflow upstream side; a ratio of a blade length of said blades to a diameter of the centrifugal multi-blade fan is equal to or over 0.12; an outer peripheral radius of said scroll casing expands as a logarithmic spiral, and its expansion angle is from 3.3° to 4.8°; a protrusion protruding toward said centrifugal multi-blade fan is provided on an inner wall on an outer peripheral side of said scroll casing, and has an approximately triangular shape protruding toward said centrifugal multi-blade fan when viewed from a primary flow direction of the air flowing through said airflow passage. 